To list the elements/devices in a metric family the first thing you need to do is get the internal metric family name. To get the internal metric family name go to Administration -> data aggregator -> monitoring configuration -> metric families then hover over the name column header and click the gear icon and select columns and click the check box for internal name. Then use this metric family internal name in the xml below. The internal name in the below xml example is "NormalizedPortInfo". Replace this with the internal name of the metric family you want to list.
<FilterSelect xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="filter.xsd">
<Select use="exclude" isa="exclude">
Then do a post of the xml to http://<DA_SYSTEM>:8581/rest/devices/mfdiscoveryhistory/filtered
This will provide the list of elements/devices associated to the metric family.